Building construction using box shaped modules made of concrete has certain advantages over more conventional building methods because the prefabrication of the modules can be formed in either a factory or on one specific location at a building site and thus tolerances can be more easily controlled. The concrete building modules, sometimes referred to as "tubes", generally consist of a ceiling surface, floor surface and two or three wall surfaces. In some cases the end wall is omitted providing an open tube module and in other cases the end wall is provided having a closed tube module. The concrete module has all the necessary structural elements such as joists, beams, posts, etc. integrally formed therein, and provides a cubic space suitable for a single room or multiple rooms. Dimension limits are defined by what can be manufactured in practice, what maximum weight can be handled and what dimensions can be transported.
Concrete building modules are formed on formwork. Reinforcing in the form of mesh is generally first applied around the formwork and then concrete is sprayed in a manner sometimes referred to under the trademark "SHOTCRETING" so that thin layers of dense concrete cover vertical surfaces. Horizontal concrete surfaces are formed in the conventional manner. When concrete is sprayed onto a smooth steel surface it produces one smooth dense concrete surface that needs minimal cosmetic treatment. This is an inner surface of the building module.
The formwork presently used for forming concrete boxes or modules has to either have tapered sides to permit the concrete box to be removed or, alternatively, the formwork must be collapsible. The formwork is not ideal with tapered sides, as the inside surfaces of the concrete module are not completely level or matched. The problems with a collapsible framework is the loss of accuracy that occurs between modules when matching surface edges. The collapsing and resetting of the framework results in dimension changes from cast module to cast module.